In the field of mobile communications it is known to provide a basic architecture in which the mobile communication system comprises an access network arranged for giving radio terminals access to the communication system, and a core network that comprises entities for providing higher level communication control, such as call switching or data unit routing for data units of a given network layer protocol, such as the Internet Protocol (IP).
FIG. 1 shows an example, in which a mobile communication network comprises entities such as base stations 100 and 101, which may exchange control signalling with a control entity 102 that can provide functions such as resource allocation (e.g. channel or bearer allocation). The base stations 100, 101 belong to an access network, and can e.g. be parts of a UMTS terrestrial radio access network (UTRAN) or an Evolved UTRAN (E-UTRAN), which is also referred to as Long Term Evolution (LTE). In this case, the entities 100 and 101 can be so-called eNodeBs, and control entity 102 can in this case be a so-called Mobility Management Entity (MME).
FIG. 1 furthermore shows entities 106 and 107 that belong to the core network, and which can e.g. be appropriate gateways, such as a serving gateway (S-GW) 106 and a packet data network gateway (PDN-gateway or P-GW) 107. The elements can thus e.g. belong to an Evolved Packet Core (EPC). The control entity 102 typically also belongs to the core network.
Furthermore, FIG. 1 shows user equipment (UE) or radio terminals 103, 104 and 105 that receive access via the base stations 100 and 101.
The individual entities are connected with one another over appropriate interfaces that are selected in accordance with the underlying definitions and protocols used in the given system. For example, if the core network is an EPC and the radio access network an LTE access network, then channels 108, 109 between radio terminals and the base station 100 (eNodeB) could be LTE radio bearers, just like channel 115, whereas the base station 100 can be connected to the core network entity 106 (e.g. a service gateway) via an IP-based S1 interface that provides a channel 112. The logical interface between base stations 100 and 101 can e.g. be an IP-based X2 interface providing a channel 110. The interface between core network elements 106 and 107 (e.g. PDN-gateway) for providing channel 113 can be provided according to the S5 interface or in roaming cases the S8 interface, as e.g. described in 3GPT TS 23.401. The interfaces between control entity 102 and base stations 100 and 101 for providing channels 111 and 114 can e.g. also be an IP-based S1 interface.
FIG. 7 shows an example of a protocol hierarchy used for communication between the radio terminal/user equipment 103, the base station (e.g. eNodeB) 100, the core network entity 106 (e.g. serving gateway) and the core network entity 107 (e.g. PDN-gateway). In this example, an LTE radio bearer between the user equipment 103 and the eNodeB 100 is established in accordance with the packet data convergence protocol (PDCP) and mapped onto a tunnel established according to the GPRS tunnelling protocol (GTP), such that the LTE bearer between the user equipment 103 and the eNodeB 100 is concatenated with the GTP tunnel established between eNodeB 100 and PDN-gateway 107. In this way, IP data units from user equipment 103 are conveyed to PDN-gateway 107, i.e. the IP peer corresponding to user equipment 103. As a consequence, the PDN-gateway (more generally a dedicated data unit processing entity of the core network) can perform appropriate data unit processing, such as e.g. routing of the IP data units towards the Internet.